The demand for 2-olefin rich feeds has recently increased. For example, 2-butene-rich feeds have been found to be useful in the production of alkylate prepared by alkylation of isoparaffins with light olefins. The desirability of using butene-2 as compared to butene-1 as feedstock to an alkylation zone to produce high octane gasoline blending stocks is disclosed in U.S. Pat. No. 2,804,490. U.S. Pat. No. 3,800,003 presents a process in which a feed stream comprising butene isomers is passed into an isomerization zone to increase the quantity of butene-2 available for passage into a downstream alkylation zone. U.S. Pat. No. 4,918,255 discloses an alkylation process using a heterogeneous isoparaffin/olefin alkylation catalyst, e.g. BF.sub.3 /Al.sub.2 O.sub.3, wherein the olefin feed is isomerized to reduce alpha olefin content using as isomerization catalyst alumina, silica, zirconia, chromium oxide, boron oxide, thoria, magnesia, aluminum sulfate or combinations thereof, as well as boron halide-modified metal oxide.
Double bond isomerization of olefins such as butene in the presence of catalysts of the pentasil type such as ZSM-5 and ZSM-11 at temperatures of 100 to 500.degree. c is disclosed in European Patent Application 0 129 899 to Hoelderich.
European Patent Application 0 247 802, to Barri et al. discloses restructuring olefins using tectometallosilicates of the Theta-1 type (ZSM-22) as well as ZSM-23 at relatively high reaction temperatures of 200 to 550.degree. C. Table 4 thereof shows 1-butene to 2-butene selectivity (mol/mol) of Theta-1 catalyst in the conversion of 1-butene of 92.1% at 234.degree. C. at 100 MPa pressure using an 11.5.+-.2.8% vol/vol 1-butene in nitrogen feed. By-products, especially isobutylene, are formed with a selectivity of 7.9%. The composition of the linear butenes in the product is 16% 1-butene and 84% 2-butene.
U.S. Pat. No. 4,749,819 to Hamilton, Jr. exemplifies double bond isomerization of an alpha olefin feed (preferably C.sub.12 to C.sub.18) to produce a product having interior double bond isomerization using a ferrierite catalyst. The reference further teaches at column 5, lines 15 to 19, that "[o]ther aluminosilicates may be exemplified by ZSM-12, ZSM-22, ZSM-23 and ZSM-48." It is not unexpected that a wide variety of catalysts can be used to isomerize 1-butene at high initial activity inasmuch as the double bond shift is one of the most facile among the hydrocarbon reactions. The thermodynamics of the reaction indicate that enhanced selectivity for 2-butenes occurs at lower temperatures and that relatively great selectivities are possible with a wide variety of catalysts at such temperatures. However, catalyst stability is known to decrease as temperatures are lowered. At lower temperatures, zeolite isomerization catalysts are known to "age" or lose their high level of activity with time. This has been attributed to the formation of undesirable carbonaceous deposits or "coke" on the catalyst's active sites during hydrocarbon conversion reactions. Once the carbon deposits have reached the point where the reaction level becomes economically undesirable, the only known way to correct the problem has been to shut down the reactor and burn the carbon off of the catalyst in an oxygen-containing atmosphere. This, needless to say, is an expensive operation which should be avoided unless absolutely necessary.
Accordingly, it would be desirable to provide a method for isomerizing 1-olefin feeds to 2-olefin rich products over a catalyst which exhibits not only high 1-olefin conversion and 2-olefin selectivity, but high stability at low temperatures as well. It would also be desirable to provide an isomerization method which not only has high selectivity for 1-olefin to 2-olefin, but a low rate of catalyst deactivation as well, resulting in long cycle times between catalyst regeneration.